For centuries, blacksmiths have known that plunging red-hot metal into cold water can transform its properties, making a blade harder, tougher or more resilient. Battery researchers have now applied a similar principle at the atomic scale, fast-quenching heated battery components to engineer beneficial defects that help them outperform flawless counterparts.
“We found that such treatments—more commonly used on thermoelectric materials—are also effective for creating atomic vacancies that enhance a material’s electrochemical properties,” said Zhi Wei Seh, a Senior Principal Scientist II at the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
These vacancies may help solve a design challenge with magnesium-ion batteries (MIBs), which offer cheaper, safer and more easily sourced alternatives to lithium-ion (Li-ion) batteries for large-scale energy storage. Currently, the few promising materials for MIB cathodes include transition metal chalcogenides (TMCs): compounds of metals with sulphur or similar elements, with high theoretical energy capacities.
But in practice, parasitic side reactions often undermine MIBs with TMC cathodes. When these batteries are charged and discharged, intermediate molecules known as magnesium polysulphides dissolve and 'shuttle' between electrodes, draining battery capacity and destabilising it.
Seh, Senior Scientist Jianbiao Wang and other A*STAR IMRE researchers worked with the A*STAR Institute of High Performance Computing (A*STAR IHPC); Nanyang Technological University, Singapore; Stanford University, US; and the Synchrotron Light Research Institute, Thailand, to develop a TMC system that would mitigate this issue.
“We selected titanium sulphide (TiS3) as our model system as theoretical calculations suggested that its intermediate phase (TiS2) had strong adsorption toward magnesium polysulphides, effectively suppressing their dissolution and shuttling,” said Wang, the study’s first author.
To unlock this potential, the team prepared TiS3 nanobelts—thin and flat crystals less than a micrometre wide—with an exposed facet in identical directions. These were then plunged from high temperatures into ice water within seconds.
“This kinetic ‘freezing’ prevents structural relaxation and defect annihilation, preserving the sulphur vacancies formed at elevated temperatures,” Seh explained.
Electron microscopy, spectroscopy and density functional theory calculations revealed these vacancies tackled two problems at once: widening pathways for magnesium ions to move more easily through the material and creating charged sites that trap polysulphide intermediates.
When tested as cathodes, the defective nanobelts also demonstrated an unexpected hybrid energy storage mechanism: first transforming from TiS3 to TiS2 while releasing magnesium sulphide, then storing additional magnesium inside the TiS2 lattice. “The most surprising aspect was that the nanobelts maintained their morphology throughout the discharge and charge process,” Wang noted.
The TiS3 cathode achieved an discharge capacity of 717.3 mAh g-1 at 25 mAh g-1 and retained 291.5 mAh g-1 after 100 cycles at a higher current density, surpassing previously reported TMC-based cathodes in MIBs. Scaled up to pouch cells, it delivered an energy density of 220 Wh kg⁻¹, putting it within range of commercial Li-ion designs. It also performed well in Li-ion, sodium-ion and aluminium-ion batteries.
“This cross-compatibility highlights the intrinsic versatility of defective polyanion cathodes,” Seh added.
Challenges remain, including sluggish magnesium-ion diffusion kinetics and the lack of stable, high-voltage-compatible electrolytes. The team aims to optimise MIB electrolyte chemistry to further suppress polysulphide shuttling and push MIBs closer to practical deployment.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE) and A*STAR Institute of High Performance Computing (A*STAR IHPC).
